Thermally activated transport of physiologically active compounds

This survey concerns the potential inherent in the conformational transition of macromolecules that occurs at an LSCT for the targeted transport of physiologically active compounds linked to these macromolecules. Methods for controlling the LSCT of the polymeric carrier are discussed, and relationships between the biological activity of the compounds being transported and their structure and the structure of the polymeric carrier are examined. Approaches ensuring conservation of biological activity via the repeated transition through LCST and providing removal of all components of the system from a living organism are considered.     

Coherent transport through spin-crossover single molecules

Coherent quantum transport calculations were performed for high- and low-spin states of a mononuclear Fe(II) complex showing spin-crossover behavior using density functional theory methods combined with the non-equilibrium Green functions procedure. The high-spin state has a larger conductivity than the low-spin state; furthermore, it behaves as a spin filter, giving a β-polarized current.     

Redox-gated electron transport in electrically wired ferrocene molecules

We have synthesized cysteamine-terminated ferrocene molecules and determined the dependence of the electron transport properties of the molecules on their redox states by measuring the current through the molecules as a function of the electrode potential. The current fluctuates over a large range, but its average value increases with the potential. We attribute the current fluctuation and its increase with the potential to the switching of the molecules from low-conductance reduced state to high-conductance oxidized state.     

Thermally activated and non-activated charge transport processes in the oxides NaxMo2

The electrical properties of Na_xM_1+yO₂ (M=Mn,Co) were measured as a function of temperature under conditions of thermodynamic equilibrium for a quenched defect structure. The results of electrochemical studies of Na_xM_1+yO₂ are also presented. A correlation is demonstrated between the structures of the ionic and electronic defects in these materials and the potential changes of the cathode in Na/Na⁺/Na_xM_1+yO₂.The author is grateful to Prof. S. Mrowec and Dr. A. Stoklosa for helpful discussions.     

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence molecules (TADF) molecules have been found to undergo efficient intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, which benefit their successful applications in organic light emitting diodes (OLEDs). Due to their long-lived delayed fluorescence, TADF molecules can also be applied in time-resolved luminescence imaging. Besides their special singlet properties, their excited triplet characteristics provide their potential applications in triplet-triplet annihilation upconversion (TTA-UC), photodynamic therapy (PDT) and organic photocatalytic synthesis by used as a triplet photosensitizer.     

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence (TADF) organic molecules feature with long-lived delayed fluorescence, because they can undergo not only efficient intersystem crossing (ISC), but also efficient reverse intersystem crossing (RISC) at room temperature. As a new type of luminescent molecules, they have exhibited successful applications in organic light emitting diodes (OLEDs). Aside from OLEDs, they are also found to have potential applications in time-resolved luminescence imaging based on long-lived fluorescence property. Meanwhile, due to their excited triplet characteristic originated from efficient ISC, they were found to be applied in triplet-triplet annihilation upconversion (TTA-UC), photodynamic therapy (PDT) and organic photocatalytic synthesis. This review briefly summarizes the characteristics and excellent photophysical properties of TADF organic compounds, then covers their applications to date aside from OLEDs based on their highly efficient ISC ability and RISC ability at room temperature.     

Direct approach for the electron transport through molecules

A very simple, straightforward, and easy to implement fully ab initio procedure for the determination of current-voltage characteristics in molecular junctions is presented. Application of this procedure predicts reasonably well the experimental findings for low bias voltages of a break junction experiment and can help us to characterize its geometry.     

Theoretical analysis of electron transport through organic molecules

We present a theoretical study of electron transport through a variety of organic molecules. The analysis uses the Landauer formalism in combination with complex bandstructure and projected densities of states calculations to reveal the main aspects of coherent electronic transport through alkanes, benzene-dithiol, and phenylene-ethynylene oligomers. We examine the dependence of the current on molecule length, the effects of molecule-molecule interactions from film packing, differences in contact geometry, and the influence of phenyl ring rotation on the conductances of phenylene-ethynylene oligomers such as 1,4-bis-phenylethynyl-benzene.     

Contact atomic structure and electron transport through molecules

Using benzene sandwiched between two Au leads as a model system, we investigate from first principles the change in molecular conductance caused by different atomic structures around the metal-molecule contact. Our motivation is the variable situations that may arise in break junction experiments; our approach is a combined density functional theory and Green function technique. We focus on effects caused by (1) the presence of an additional Au atom at the contact and (2) possible changes in the molecule-lead separation. The effects of contact atomic relaxation and two different lead orientations are fully considered. We find that the presence of an additional Au atom at each of the two contacts will increase the equilibrium conductance by up to two orders of magnitude regardless of either the lead orientation or different group-VI anchoring atoms. This is due to a resonance peak near the Fermi energy from the lowest energy unoccupied molecular orbital. In the nonequilibrium properties, the resonance peak manifests itself in a negative differential conductance. We find that the dependence of the equilibrium conductance on the molecule-lead separation can be quite subtle: either very weak or very strong depending on the separation regime.     

Thermally activated conduction in molecular junctions

We report temperature dependence measurements on the conductance of individual molecular wires. The results show for the first time in a molecular junction the theoretically predicted transition from coherent superexchange tunneling conductance to an activated hopping mechanism as temperature is increased.     

Variations of diffusion coefficients of redox active molecules in room temperature ionic liquids upon electron transfer

In ionic liquids, the diffusion coefficients of a redox couple vary considerably between the neutral and radical ion forms of the molecule. For a reduction, the inequality of the diffusion coefficients is characterized by the ratio gamma = D(red)/D(ox), where D(red) and D(ox) are the diffusion coefficients of the electrogenerated radical anion and of the corresponding neutral molecule, respectively. In this work, measurements of gamma have been performed by scanning electrochemical microscopy (SECM) in transient feedback mode, in three different room temperature ionic liquids (RTILs) sharing the same anion and with a series of nitro-derivative compounds taken as a test family. The smallest gamma ratios were determined in an imidazolium-based RTIL and with the charge of the radical anion localized on the nitro group. Conversely, gamma tends to unity when the radical anion is fully delocalized or when the nitro group is sterically protected by bulky substituents. The gamma ratios, standard potentials of the redox couple measured in RTILs, and those observed in a classical organic solvent were compared for the investigated family of compounds. The stabilization energies approximately follow the gamma ratios in a given RTIL but change considerably between ionic liquids with the nature of the cation.     

Thermally activated crystallization of two FeNiPSi alloys

The crystallization kinetics of two alloys in the Fe-Ni-P-Si quaternary system have been investigated, with both isothermal and continuous heating experiments, by means of differential scanning calorimetry. Both alloys present two separated crystallization processes. The Johnson-MehlAvrami-Erofeev equation with a rate constant following the Arrhenius behavior gives the best fit of the experimental data. In all processes the value of its JMAE kinetic exponent is not constant. In the nearly stages, n changes steeply revealing the transient nucleation effect to reach values corresponding to a three-dimensional volume growth controlled by diffusion in the central part (0.3<x<0.55). Latter in the transformation n continuously decreases reflecting the saturation of nucleation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Super-resolution morphological dissemination of intercalating dye in single DNA molecules via binding activated localization microscopy

Super-localization of intercalating dye YOYO-1 in single λ-DNA at super-resolution by binding activation localization microscopy (BALM).     

Electrochemical electron transfer and its relation to charge transport in single molecule junctions

Ability to control charge transport at nanometer scale lies in the heart of design of fast reliable electronic devices. Molecular electronics thrive to use functional molecules for such transport. If the molecule contains redox center(s), a diode-like or transistor-like behavior can be easily explored by controlling not only the voltage difference between two metallic contacts of the molecular junction but also the potential of one of the contacting electrodes with respect to some reference. Thus, one needs to understand the relationship between electrochemical electron transfer and charge transport in metal–molecule–metal junctions. This review presents latest theoretical approaches toward understanding of such relationship and discusses pivotal experimental works to validate them. Tunneling and hopping pathways may operate in parallel (two-channel model), but experimental conditions dictate the channel preference.     

Microvoltammetry of lithium nickel oxide single particle: deterioration of the redox behavior by water molecules

The microelectrode technique was applied to investigate the electrochemical behavior of LiNiO₂ which seriously influenced by water molecules. Cyclic voltammograms of humidified LiNiO₂ particles were compared to that of as-synthesized. As a result, a significant peak-potential shift was observed, which denotes that the reaction product caused by H₂O generates an electrochemical inactive material on the particle which prevents the Li⁺ insertion/extraction. The reaction product was considered to be NiO, and deterioration property has also been discussed.     

Electrode kinetic studies of single electron charge transfer redox couples using the faradaic rectification method

Three single electron charge transfer redox reactions have been studied using the faradaic rectification method. The kinetic parameters obtained for the ferricyanide-ferrocyanide redox couple are α=0.49, k_a⁰=12×10^?2 cm s^?1; for the chromic-chromous system α=0.47, k_a⁰=2×10^?3 cm s^?1 and for the titanic-titanous reaction α=0.49 and k_a^o=6×10^?4 cm s^?1 at 27°C.